This invention relates to a pusher cylinder for a tunnel kiln for moving kiln cars in the tunnel kiln.
Pusher cylinders have been used for many years for moving kiln cars loaded with molded ceramic green products in tunnel kilns used for sintering them. As shown by way of example in FIG. 1, a protrusion 13 is provided at a lower portion of a kiln car 12 loaded with molded ceramic green products to be sintered in a tunnel kiln 11. On the other hand, a projection 16 is provided at an outer end of a piston rod 15 of a pusher cylinder 14 and adapted to engage the protrusion 13 provided on the kiln car 12 so that the kiln car 12 is moved in the tunnel kiln 11 by driving of the pusher cylinder 14 through a distance corresponding to a stroke of the pusher cylinder 14.
With such a pusher cylinder constructed as above described, since the pusher cylinder 14 is provided near to the tunnel 11 with the aid of a rod support 17, a length of the piston rod 15 is only for example 60 cm longer than that of a stroke of the pusher cylinder 14. Therefore, part of the rod 15 to be received in the pusher cylinder 14 is also received in the tunnel kiln at different times.
Moreover, a ceramic green body generally includes an organic molding aid. Therefore, when the ceramic green body is sintered, the molding aid is decomposition by heating to produce a decomposed product, which is initially in the form of a gas or mist in a high temperature zone of the kiln, but solidifies in a low temperature zone into a tar or mist-like decomposition product which will be referred to hereinafter as "tar".
As a result, tar 18 (shown in dots on the piston rod 15 in FIG. 1) produced during sintering is attached to the piston rod 15 in the tunnel kiln 11 so that the tar 18 is carried along by the piston rod 15 into the pusher cylinder 14. The tar 18 remains in the pusher cylinder 14 and causes the pusher cylinder 14 and a packing 19 for a piston within the cylinder to be seriously damaged.